This invention relates to magnetic induction type pickups for guitars and other stringed musical instruments, and deals more particularly with such a pickup having an improved ability to suppress hum or other noise arising from stray magnetic fields and also to suppress the production of microphonic type output signals.
Magnetic induction type pickups establish a magnetic flux circuit passing in part both through a string of the associated instrument and through an associated coil, and operate on the principle that as the string vibrates, the reluctance of the flux circuit is varied to vary the magnetic flux through the coil and to thereby generate a signal voltage in the coil. Unfortunately, electric motors, and many other pieces of common electrical apparatus tend to emit stray magnetic fields, and when magnetic induction type pickups are used in their vicinity, the stray fields often tend to couple with the pickup to produce a noise factor in the output signal of the pickup reproduced as audible noise in the output from the amplifier and speaker system driven by the pickup. Due to the very common use of 60Hz alternating current power, the stray magnetic fields in question commonly have a 60Hz frequency and in coupling with the pickup produce a 60Hz audible hum from the associated speaker.
Another problem often encountered with magnetic induction pickups is that sound vibrations in the air may be transmitted to the pickup and may set one or more internal parts of the pickup into resonant vibration to produce accompanying flux changes and output signals at the resonant frequency which, through positive feedback, sustain the resonant vibration and produce microphonic or squealing sounds from the speaker or speakers.
The general object of this invention is, therefore, to provide a magnetic induction type pickup for a stringed musical instrument which minimizes hum and other noise in its output signal by suppressing the effect of stray magnetic fields regardless of the direction of such fields and which pickup despite such noise suppressing quality nevertheless yields a high quality output signal voltage in response to the vibration of the instrument strings.
Another general object of the invention is to provide a magnetic induction type pickup for a stringed musical instrument wherein resonance of various internal parts is suppressed to avoid microphonics.
Other objects and advantages of the invention will be apparent from the accompanying drawings and from the following written description.